The polymerase chain reaction (PCR) is a process where a single DNA molecule can be amplified (replicated) by orders of magnitude into thousands or millions of copies of the molecule. The process relies on cycling a PCR mixture containing polymerase, dNTPs (deoxyribonucleotides), sample DNA template, and primers through different temperatures. At a first, high-temperature range, denaturation occurs as the paired strands of the double-stranded sample DNA template separate into two individual strands. At a second, low-temperature range, annealing of primers complementary to the region of the sample DNA template being targeted for amplification takes place. At a third, mid-temperature range, extension of the complementary sequence from the primer occurs, during which the polymerase adheres to the primer and uses nucleotides to replicate each isolated sample DNA template strand. This cycle is typically repeated (e.g., from 20-40 times) to increase the amount of replicated DNA on an exponential basis until the desired amount is present for a particular experiment. In general, the PCR amplification process has become an indispensable part of genetic analysis in various areas including molecular biology, diagnostics, forensics, agriculture, and so on.
Efforts to reduce the time and costs associated with the PCR process are ongoing. One area of development is in microfluidic devices which provide a miniaturized environment for the PCR process that enables a reduction in both the volume of PCR mixture and the time needed for PCR temperature cycling. Small devices such as microfluidic chips have a reduced thermal mass that enables the mixtures to be cycled through different temperatures in the denaturing, annealing and extending steps at increased speeds, which reduces the overall time needed for completing the PCR process. In addition, increased integration in PCR systems that include such microfluidic chips has resulted in the use of microfluidic mixers, valves, pumps, channels, chambers, heaters and sensors. However, the pumping and mixing components in such systems are typically not integrated into the microfluidic chips themselves. Instead, these components are generally external to the microfluidic chip, which increases the size of the integrated system and raises the costs of fabrication.